WO2006104015A1

WO2006104015A1 - Ball screw

Info

Publication number: WO2006104015A1
Application number: PCT/JP2006/305850
Authority: WO
Inventors: Daiju Takahashi
Original assignee: Nsk Ltd.
Priority date: 2005-03-25
Filing date: 2006-03-23
Publication date: 2006-10-05
Also published as: JPWO2006104015A1; EP1862707A4; EP1862707A1; US20090007710A1

Abstract

A ball screw suitable for use under high load, which is used particularly in an electric injection molding mechanism and in which damage and wear of balls are reduced as compared to conventional products to provide the ball screw with long lifetime and high reliability. The ball screw is characterized in that the balls have surface hardness higher than that of a ball groove of a screw shaft and that of a ball groove of a nut, and that a solid lubricant film having a thickness of not less than 1 μm and not more than 5 μm is formed on the surface of the balls. The grooves (11, 21) of the screw shaft (1) and the nut (2) have a Gothic arch-like cross-section. The ratio (R/D) of the radius (R) of the cross-sectional circular arc of the groove (11) to the diameter (D) of a ball (2) is set to not less than 51.0% and not more than 52.0%. A solid lubricant coating composed of MoS2 and having a thickness of not less than 0.5 μm and not more than 3.0μm is formed on the surface of a ball (3).

Description

Specification

Ball screw

Technical field

TECHNICAL FIELD [0001] The present invention relates to a ball screw, and particularly for an actuator, for example, a ball screw and a linear guide that are used in industrial machines such as an electric injection molding machine and a press machine and are used at high loads. It relates to a linear motion device such as.

Background art

Ball screws used in electric injection molding apparatuses, electric press apparatuses, and the like are used under severe conditions under extremely short loads and reciprocating movements with a relatively short stroke. Therefore, the peeling life due to repeated stress on the raceway surface becomes a problem. As countermeasures, in general, the ball diameter is made as large as possible, the radius of curvature of the raceway surface is made as close as possible to the ball diameter, and the contact surface pressure is lowered to suppress repeated stress values, thereby reducing the required life. It will be fulfilled.

However, in the case of a ball screw, unlike a ball bearing or a linear guide, the slip component is large due to a geometric problem that the ball rolls on a spiral track. Due to the size of the sliding component, in a general ball screw with a lead angle of 15 degrees or less, the ratio of the radius (R) of the arc that forms the cross section of the groove to the ball diameter (D) (RZD) 52% In the following, as represented by white peeling, there was a problem that the life would be shortened, so R / D was usually set to 52% or more and 54% or less.

[0004] The first background art is a relatively large ball screw used in a conventional electric injection molding machine, a press machine, etc., and a high load. It is used in the harsh condition where it is used in a rooke, and after stopping once with the maximum load applied, it moves backwards and backwards.

[0005] Further, as a feature of the ball screw used in these machines, there is an attachment error of the ball screw attached to the machine base. That is, a relatively large mounting error is assumed between the ball screw and the machine base. Due to this mounting error, a relative twisting moment is generated between the screw shaft and the nut, resulting in a revolution speed difference between the balls and the balls competing with each other. They collide and collide, causing damage, wear, and even peeling. As a result, the generated metal powder mixes with the grease and acts as a foreign substance, resulting in premature peeling of the screw shaft and ball screw groove (rolling surface) of the nut.

[0006] In addition, a force that forms an oil film on the ball surface or the rolling surface by the encapsulated grease. Since the collision between the balls is a collision between the convex shape and the convex shape, the collision between the rolling surface and the ball (concave shape) Compared to the collision with a convex shape), it is difficult to form an oil film, and it is easy to cause a metal contact immediately after the oil film is cut.

[0007] In order to eliminate such a problem, the ball surface hardness of the ball screw that secures positioning accuracy by applying a preload between the ball and the ball screw groove of the screw shaft and the ball screw groove of the nut is increased. The wear resistance of the ball is improved by making it higher than the surface hardness of the ball screw groove of the screw shaft and the ball screw groove of the nut (see Patent Document 1).

) o

[0008] In addition, fine particles of molybdenum disulfide (MoS) are sprayed onto the ball screw ball, the ball screw groove of the screw shaft, and the ball screw groove of the nut, and fixed by collision to lubricate the film with a thickness of 0.5 m or less.

2

A film is also formed to improve wear resistance!

In Patent Document 2, fine particles of molybdenum disulfide molybdenum are sprayed and fixed to at least one sliding contact portion of a screw shaft screw groove, a nut screw groove, and a ball. Ball screws with a lubricant coating with a dimension of 0.5 μm or less have been proposed.

[0009] It is described that, when the thickness is 0.5 m or less, the adhesion of the coating to the sliding contact portion is improved, and the coating is difficult to peel off, and the dimensional change can be suppressed even when peeled off. Yes.

[0010] As a second background art, an example of a conventional ball screw is shown in FIGS. 14 (perspective view) and 15 (sectional view). This ball screw is a tube-type ball screw using a tube as a return path of the ball, and includes a screw shaft 101, a nut 102, a ball 103, and a tube 104. Reference numeral 106 in FIG. 14 is a tube presser for fixing the tube 104 to the nut 102. In FIG. 15, the tube retainer 106 is not shown.

Helical grooves 111, 121 are formed on the outer peripheral surface of the screw shaft 101 and the inner peripheral surface of the nut 102, and the track K of the ball 103 is formed by these grooves 111, 121. And Bo When the nut 103 rolls on the track K in a loaded state, the nut 102 moves linearly relative to the screw shaft 101.

[0011] The tube 104 is formed in a substantially portal shape, and both ends thereof are inserted into through holes 122 provided in the cylinder forming the nut 102, and the screw shaft 101 is connected so as to connect the start point and the end point of the track rod. It is arranged diagonally across. Therefore, the ball 103 that has reached the end point of the track を通 is returned to the start point of the track を通 through the tube 104. In this example, since there are two ball circulation paths (trajectory + return path), two tubes 104 are provided.

[0012] Ball screws for electric injection molding machines and press machines are relatively large and receive high loads.

Specifically, a high load is momentarily applied, the stroke is used with a short stroke, and after resuming the rotation with the maximum load applied, the reciprocating motion that reversely rotates is repeated. Since it is used under such harsh conditions, a ball screw for the above-mentioned use has been conventionally used with a single nut and a very small assembly clearance (about 1Z400 as a ratio to the ball diameter). To increase the load capacity of the ball screw and extend its service life, the ratio of the radius (R) of the cross-section arc of the grooves 111 and 121 (of the screw shaft 101 and nut 102) to the diameter (D) of the ball 103 ( RZD) may be made smaller than the conventional 52.0 to 54.0%.

However, in this method, the longer axis of the contact ellipse between the ball and the groove forming the track becomes longer than that of the conventional ball screw, and the slip component becomes larger. Along with this, since the tangential force in the contact ellipse increases, it is impossible to deny the possibility of surface-origin separation or internal origin delamination due to white texture. In addition, since the ball screw has a slower rolling speed than a general rolling bearing such as a ball bearing, it is difficult to form an oil film. Therefore, when the ratio (RZD) is made smaller than 52.0 to 54.0% with a ball screw, it is necessary to take measures to prevent premature damage.

[0014] As conventional examples of measures for improving the lubrication characteristics of the ball screw, the following may be mentioned.

Patent Document 3 below describes that a specific grease is used to prevent early peeling of the ball screw used in the drive system of the electric injection molding machine.

In Patent Document 4 below, at least a part of the rolling friction surface and sliding friction surface of a machine part using a ball is softened with gold, silver, lead, zinc, tin (Sn), indium or the like. It is disclosed that fine particles made of carbonaceous metal, polytetrafluoroethylene (PTFE), perfluoroalkoxy fluorine resin (PTA), etc. are sprayed together with air from a nozzle cover to form a solid lubricating film. Yes.

(See Patent Document 2)

[0015] As a third background art, in machine tools such as machining centers and industrial robots, in order to smoothly convert the rotational motion to linear motion and to move the linear motion of the work table smoothly, Linear motion devices using balls or rollers as balls are often used.

FIG. 1 is a top view showing an example of a ball screw which is one of linear motion devices, and FIG. 2 is a cross-sectional view taken along AA in FIG. As shown in the figure, the ball screw 1 includes a screw shaft 3 having a male screw groove 3a formed on the outer peripheral portion, a cylindrical nut 7 which is a linear motion body having a female screw groove 5 formed on the inner peripheral surface, and a male screw. It is composed of a plurality of balls 9 interposed between the groove 3a and the female thread groove 5.

[0017] The nut 7 moves linearly along the axial direction of the screw shaft 3, and has a cylindrical shape. A flange 11 for fixing to a table (not shown) of the apparatus is formed at one end. In addition, a part of the outer peripheral surface is cut away to form a flat portion 13. A female screw groove 5 having the same shape and pitch as the male screw groove 3a is formed on the inner peripheral surface of the nut 7, and a tube 15 serving as a circulation path by connecting one end side and the other end side of the female screw groove 5 is provided. It is fixed to the flat surface portion 13 by a tube presser 17. Then, the ball 9 is transferred through the tube 15, and the ball 9 is circulated to the other end side by the force on one end side of the female screw groove 5. In addition, plastic dust seals 19 are disposed at both ends of the nut 7 to prevent foreign matter from entering the nut 7 from the outside.

[0018] In the ball screw 1, the force balls 9 configured roughly as described above collide with each other to generate noise or damage the balls 9. Therefore, as shown in the drawing, a holding piece 21 is generally inserted between the balls 9 and 9. For example, as shown in FIG. 3 (sectional view perpendicular to the axis of the screw shaft 3), the holding piece 21 in which the contact surface 11 with the ball 9 is formed in a concave spherical shape between the balls 9 and 21. Is inserted. As the material of the holding piece 21, a polyamide such as 66 nylon and a synthetic resin such as fluorine resin are generally used (see Patent Document 5).

[0019] As a fourth background art, a ball screw used in an electric injection molding machine or a press machine is relatively large and is loaded with a high load. The It is used under harsh conditions, such as when it is stopped with the maximum load applied, and then reverse rotation (reciprocating motion).

For such a ball screw, it is inevitable that a moment load acts between the screw shaft and the nut due to insufficient rigidity of the device itself in which the ball screw is incorporated. If a ball screw is used in a state where a twisting moment load is applied, the revolving speed of the ball will differ within the load region, so the ball return path (formed by the screw groove of the screw shaft and the screw groove of the nut) The end point force of the ball rolling path may cause clogging of the ball in the path where the ball is circulated by sending it to the start point. Further, since the ball moves while moving in a staggered manner in the ball return path, the ball moves while being rubbed against the inner surface of the ball return path.

Furthermore, such a ball screw is designed such that the diameter of the ball is larger than the diameter of the screw shaft in order to increase the load capacity. Therefore, as the ball diameter increases, the kinetic energy of the ball also increases, and the influence of the ball on the ball return path increases.

If the ball moves while being rubbed against the inner surface of the ball return path with an excessive force, the inner surface of the ball return path may be worn or peeled off, resulting in poor circulation of the ball. In addition, since the wear powder and peeling powder act as foreign matters, early peeling occurs in the thread groove and the ball, and the ball screw may have a short life.

[0021] As a countermeasure against such a problem, a ball screw has been proposed in which the inner surface roughness of the circulation tube corresponding to the above-described ball return path is an arithmetic average roughness of 0.2 mRa or less. With such a configuration, the generation of dust such as metal powder accompanying the contact between the inner surface of the circulation tube and the ball is suppressed, so that the amount of foreign matter entering between the thread groove and the ball can be suppressed. (See Patent Document 6)

[0022] Furthermore, a ball screw is disclosed in which a circulating member corresponding to the above-described ball return path is formed of a solid lubricant. Such a ball screw can be suitably used in an environment where normal lubrication with a lubricating oil or grease is difficult. (See Patent Document 7)

Patent Document 1: JP 2000-346162

Patent Document 2: JP 2004-60742 A Patent Document 3: Japanese Patent Laid-Open No. 2001-49274

Patent Document 4: Japanese Patent Laid-Open No. 6-109022

Patent Document 5: Japanese Patent Laid-Open No. 11 315835

Patent Document 6: Japanese Unexamined Patent Application Publication No. 2004-92787

Patent Document 7: Japanese Patent Laid-Open No. 62-283252

Disclosure of the invention

Problems to be solved by the invention

[0023] As a first problem, in the conventional general ball screw, RZD is set to 52% or more and 54% or less, but it is extremely large required for a ball screw in an electric injection molding device or an electric press device. As a result, it becomes impossible to sufficiently suppress the surface pressure against the load, and as a result, peeling damage (peeling due to fatigue life) due to repeated stress on the raceway surface occurs early, and the required life is not satisfied. there were.

[0024] In addition, in order to provide a sufficient life against peeling damage due to rolling fatigue life by sufficiently suppressing the generated surface pressure and repetitive stress of the raceway surface, the ball surface with RZD of 52% or less is used. The problem is that the life of the ball is shortened due to the effect of sliding between the ball and the ball.

[0025] As a second problem, the screw shaft and the ball screw groove of the nut are usually moved in the axial direction while rotating the general-purpose mortar formed in a predetermined cross-sectional shape, so that the mortar shape is changed. Complete grinding is performed by transferring and grinding. Therefore, the surface roughness in the perpendicular direction where the turret shape is transferred as it is compared to the roughness in the axial direction is considerably rough, and the surface roughness is generally about 0.3 m. In contrast, balls are finished to a surface roughness of about 0.006 μm. Therefore, as in Patent Document 1, damage and wear of the ball cannot be avoided simply by making the surface hardness of the ball higher than the surface hardness of the ball screw groove of the screw shaft or the ball screw groove of the nut.

[0026] Also, in Patent Document 2, a lubricant film having a disulfide-molybdenum force is formed on the ball, the ball screw groove of the screw shaft, and the ball screw groove of the nut. Perspective power of the film The film thickness is defined as 0.5 m or less. This is a configuration in which the ball screw of Patent Document 2 applies preload and is used for applications that require high feed accuracy. In other words, the ball screw for high-load applications assumed by the present invention has a concern about durability with such a thin and lubricating coating.

[0027] The present invention has been made paying attention to such a conventional problem, and suppresses damage and wear of the ball as compared with the conventional one, and has a long life and high reliability. In particular, the electric injection molding apparatus and the electric motor An object of the present invention is to provide a ball screw suitable for a high load application used in a press device or the like.

[0028] As a third problem, since the holding piece 21 always contacts the ball 9 and moves infinitely in the circulation path while causing slippage, sliding friction between the holding piece 21 and the ball 9 is completely eliminated. First of all, it has a problem of deteriorating the operability of the ball screw 1. Such a defect is a phenomenon that occurs in general linear motion devices including the ball and the holding piece in addition to the ball screw 1.

[0029] The present invention has been made in view of such a situation, and an object thereof is to improve the operability in a linear motion apparatus including a holding piece.

[0030] As a fourth problem, since the ball screw of Patent Document 6 described above suppresses the generation of dust such as metal powder, it suppresses the early separation of the screw groove and the ball due to the entrapment of foreign matter. Although it was possible, it was difficult to sufficiently suppress the abrasion and peeling of the inner surface of the circulation tube. In addition, the ball screw disclosed in Patent Document 2 does not take measures to prevent wear and separation of the ball return path. Furthermore, since the ball screw of Patent Document 7 is not strong enough for the circulating member made of solid lubricant, when used under conditions where a high load is applied and a moment load is applied, There was a risk of damage to the circulation member or malfunction of the ball screw.

Therefore, the present invention solves the problems of the conventional ball screw as described above, and even when used under conditions in which a high load is applied and a torsional moment load acts, wear, separation, etc. It is an object of the present invention to provide a ball screw having a long life due to damage.

Means for solving the problem

[0031] To achieve the above object, the present invention has the following constitutional power as the first constitution.

(1) A screw shaft having a spiral groove formed on the outer peripheral surface and a spiral groove formed on the inner peripheral surface A nut, a raceway in which the screw shaft groove and the nut groove are formed to face each other, a return path connecting the end point and the start point of the raceway, a plurality of paths arranged in the return path and in the track A ball screw having a ball,

At least one of the screw shaft and nut

The ratio (R / D) of the radius (R) of the arc forming the cross section of the groove to the diameter (D) of the ball is 51.0% or more and less than 52.0%,

A ball screw, wherein a solid lubricant film is formed on at least a surface of at least one of the ball itself or a part in contact with the ball.

[0032] Further, the present invention has the following constitutional power as the second constitution.

(2) a screw shaft having a ball screw groove on the outer peripheral surface, a nut fitted to the outer periphery of the screw shaft and having a ball screw shaft facing the ball screw groove of the screw shaft on the inner peripheral surface; A ball rolling path composed of a ball screw groove of the screw shaft and a ball screw groove of the nut and a ball screw groove provided on the nut, and communicated with a part of the ball rolling path and another part of the ball rolling path. A connection path, a ball circulation path constituted by the connection path and the ball rolling path, and a plurality of balls accommodated so as to be endlessly arranged in the ball circulation path; The surface hardness of the ball is higher than the surface hardness of each of the ball screw groove of the screw shaft and the ball screw groove of the nut, and 1 μm or more on the surface of the ball. A solid lubricant film is formed with a film thickness of μm or less. To (1), wherein the ball screw.

(3) The ball screw as described in (2) above, wherein the solid lubricant film is made of molybdenum disulfide or soft metal force.

(4) The ball screw according to (3), wherein the soft metal is selected from tin, gold, silver, zinc, indium, and their respective alloy forces.

(5) The ball screw according to any one of (2) to (4), wherein the surface hardness of the ball is HRC63 or more.

[0033] Further, the present invention has the following constitutional power as the third constitution.

(6) At least one of the screw shaft and the nut has a Gothic arc cross section of the groove (a shape in which two arcs having the same radius and different centers are connected), and the diameter of the ball (D The ratio (RZ D) of the radius (R) of the circular arc is 51.0% or more and less than 52.0%, and the screw shaft groove or nut groove And at least one of the balls has a solid lubricant film formed on a surface thereof.

(I) The ball screw described.

[0034] According to this ball screw, for at least one of the screw shaft and nut, the groove has a Gothic arc cross section, and the ratio (RZD) is 51.0% or more and 52.0% or less. , Can increase the load capacity. In addition, along with this, the long axis of the contact ellipse between the ball and the groove forming the track becomes longer, and the slip component increases, but at least one of the screw shaft groove, nut groove, and ball is increased. Since a solid lubricant film is formed on the surface, good lubricating characteristics are ensured and early damage is prevented.

[0035] (7) Since the ball screw for the electric injection molding machine or press machine has a gap between the ball and the track of 5 μm or more and 70 m or less, the thickness of the solid lubricant film is 0.5 m or more. 3. Good lubrication characteristics can be obtained by using Ο μm or less.

(8) Examples of the solid lubricant film include a film made of molybdenum disulfide or tin.

(9) It is preferable that a holding piece is disposed between the balls.

[0036] Further, the present invention has the following constitutional power as the fourth constitution.

(10) a holding piece interposed between the balls, a force on one end side of the ball groove and a circulation path for circulating the ball on the other end side of the ball groove; The linear motion device according to (1) above, wherein a film made of molybdenum disulfide, a soft metal, or a polymer material is formed on at least a surface of the holding piece in contact with the ball.

[0037] The present invention has the following constitutional power as the fifth constitution.

(I I) The ball screw according to (1) above, wherein a solid lubricating film made of at least one of molybdenum disulfide and an organic molybdenum compound is coated on the inner surface of the ball return path.

[0038] (12) The ball screw according to (11) above, wherein the ball return path is made of a resin. (13) The ball screw as set forth in (11) above, wherein the ball return path is formed of a resin member manufactured by injection molding.

(14) The ball screw according to (11), wherein the ball return path is made of metal.

(15) The ball screw as set forth in (11), wherein the ball return path is made of a metal member manufactured by metal pressing.

The invention's effect

[0039] The groove R ratio was 51 to 52%, and a solid lubricant film was formed on the surface of the ball or in contact with the ball by surface coating treatment of molybdenum disulfide, soft metal, etc. The surface pressure acting on the groove can be suppressed, and the problem of short life due to the increase in the slip component that occurs due to the fact that it is a spiral groove, which is a characteristic of the ball screw, and the reduced groove R ratio is tangential. By suppressing the force, it can be solved at the same time, resulting in high load and long life

[0040] In the ball screw of the present invention, the surface hardness of the ball is higher than the surface hardness of each of the ball screw groove of the screw shaft and the ball screw groove of the nut, and further, 1 μm or more to 5 μm on the ball surface. Since the following thick solid lubricant film is deposited, damage and wear of the ball can be prevented more reliably, resulting in a long life and high reliability.

[0041] The linear motion device of the present invention operates stably over a long period of time with no malfunction due to the holding piece having a lubricating film formed on the surface in contact with the ball. .

[0042] The ball screw of the present invention has a long service life due to damage such as wear and peeling even when used under conditions where a high load is applied and a moment load is applied.

Brief Description of Drawings

FIG. 1 is a top view showing an example of a ball screw which is a kind of linear motion device.

2 is a cross-sectional view taken along the line AA in FIG.

FIG. 3 is an enlarged view taken along the thread groove of the ball screw shown in FIG. 1.

FIG. 4 is a cross-sectional view showing an example of a holding piece.

FIG. 5 is a cross-sectional view showing another example of a holding piece.

FIG. 6 is a view showing still another example of the holding piece. FIG. 7 is a perspective view showing an example of a linear guide which is another example of the linear motion device.

FIG. 8 is a torque measurement data of Example 7.

FIG. 9 shows a torque measurement data of Example 8.

FIG. 10 shows a torque measurement data according to the ninth embodiment.

FIG. 11 is a torque measurement data of Comparative Example 6.

FIG. 12 is a torque measurement data of Comparative Example 7.

FIG. 13 is a view showing a groove cross section of a screw shaft and a nut of the ball screw of this embodiment. FIG. 14 is a perspective view showing an example of a ball screw.

FIG. 15 is a cross-sectional view showing an example of a ball screw.

FIG. 16 is a partial cross-sectional view showing an example of a ball screw having a holding piece.

FIG. 17 is a cross-sectional view showing an example of a holding piece.

FIG. 18 is a cross-sectional view showing an example of a holding piece.

FIG. 19 is a cross-sectional view of a principal part showing a peripheral portion of an end portion of a tube.

Explanation of symbols

1 Bonore screw

3 Screw shaft

3a Male thread groove

5 Female thread

5a Female thread groove

7 Nut

9 balls

15 tubes

21 holding piece

23 Concave

77 ball rolling path

101 Screw shaft

111 Screw shaft groove (spiral groove)

102 Natsu 121 Nut groove (spiral groove)

122 Nut through hole

103 balls

104 Tube (return path)

107 holding piece

170 holding piece

K orbit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the ball screw of the present invention will be described in detail with reference to the drawings.

(First embodiment)

[0046] In the present invention, the type and configuration of the ball screw itself are not limited. However, the ball screw itself is used in a relatively large and high load, such as used in an electric injection molding machine or a press machine. The ball screw is the main target. An example of a ball screw is shown in FIG. 1 (top view) and FIG. 2 (cross-sectional view of FIG. 1). As shown, the ball screw 1 has a male screw groove 3a formed in a spiral shape on the outer periphery thereof. Ball rolling formed by a cylindrical nut 7 in which a screw shaft 3 and a female screw groove 5a facing the male screw groove 3a are spirally formed on the inner periphery thereof, and a male screw groove 3a and a female screw groove 5a A number of balls 9 interposed in the road are the main components. The nut 7 is formed with a flange 11 for fixing to a table or the like (not shown) at one end, and a flat surface (notch surface) 13 is cut on a part of the outer peripheral surface (upper side in FIG. 2). . Further, a pair of front and rear steel tube tubes 15 serving as a circulation path for the balls 9 are fixed to the nut 7. It has a structure that circulates through. In the figure, reference numeral 17 denotes a tube presser for fixing the tube 15 on the flat surface 13 of the nut 7, and reference numeral 19 denotes a dust-proof plastic sheath attached to both ends of the nut 7. Speak.

[0047] In the present invention, the surface hardness of the ball 9 is set to be higher than the surface hardness of each of the male screw groove 3a and the female screw groove 5a. If the surface hardness of the ball 9 is a relatively set force HRC63 or more, damage and wear can be further suppressed. In order to satisfy this relationship of surface hardness, each material of ball 9, screw shaft 3 and nut 7 can be selected or surface treatment such as heat treatment can be performed. Just give it.

[0048] Further, on the ball 9, a lubricant film having a molybdenum disulfide or soft metal force is formed.

As the soft metal, tin, gold, silver, zinc, indium and alloys thereof are preferable from the viewpoint of lubrication effect and film formability. The film thickness of the lubricant film should be 1 μm or more and 5 μm considering high load applications. If the film thickness is less than 1 m, it may be inferior in durability when used for high load applications. In general, ball screws for high-load applications do not require the dimensional accuracy of the ball 9 as much as the ball screw (see Patent Document 2) that increases the feed accuracy by applying a preload. ヽ Force Lubricant coating exceeds 5 / zm It will come in trouble. Note that molybdenum disulfide and soft metal that form a lubricant film are solid lubricants, and therefore, even if they are peeled off, they are mixed into the grease and exert a lubricating action.

[0049] Although there is no limitation on the method of forming the lubricating film on the ball 9, the shot-peening method is suitable for forming a relatively thick film as described above while controlling the film thickness. . In this shot peening method, a small sphere called a shot material with a particle size of several tens / zm is accelerated and injected from the projection device toward the surface to be processed, and the small sphere collides with the surface to be processed at high speed. In the present invention, molybdenum disulfide molybdenum or a soft metal is used for the shot material and is sprayed toward the surface of the ball 9.

[0050] In general, the shot-peening method tends to roughen the coating surface. Therefore, the surface of the lubricating coating may be smoothed as necessary.

Example

[0051] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0052] [Examples 1 to 5, Comparative Examples 1 to 4]

Various balls with different surface hardness and lubricating coating are incorporated into a ball screw manufactured by Nippon Seige Co., Ltd. (specifications are as follows), and a durability test is performed with a ball screw durability tester manufactured by Nippon Seie Co., Ltd. The lifespan was compared. The film was formed using a commercially available shot peening machine.

• NIPPON SEI Co., Ltd. ball screw “BS6316—10.5 (W: 63 X 16 X 300-Ct7) • Shaft diameter: 65mm

• Li ~~ do: 16mm

• BCD: 65mm

'Ball diameter: 12.7mm

• Effective number of turns: 3.5 turns x 3 rows

• Screw shaft and nut materials · Heat treatment: SCM420H · Carburizing heat treatment

• Hardness of rolling surface of screw shaft and nut: HRC62

• Ball screw dynamic load rating, Ca: 450kN

'Test load: 300kN (0. 67Ca)

• Crying moment: 4.2 kN-m

'Lubrication: Lube Co., Ltd. YS2 grease is automatically supplied by an automatic lubricator.

[0053] In the durability test, the ball screw was periodically disassembled, and the travel distance until separation occurred in either the ball or the raceway groove was determined. The life of the ball screw was judged at the time when peeling occurred. Table 1 shows the test results. In Table 1, the life is the life ratio of Comparative Example 1, that is, assuming that the life of the conventional ball screw for high load application actuator is 1.

[0054] [Table 1]

The examples in Table 1 assume an RZD ratio of 52%.

Example 1 is a specification in which a 1.2 ^ πι (Μο8 film is formed on a ball having a surface hardness of HRC64

2

The service life was 1.68 times longer, and peeling occurred on the rolling surface of the screw shaft. In Example 2, a 4.8 m MoS film was formed on a ball with a surface hardness of HRC63.

2

The service life was 1.72 times longer, and the screw shaft rolling surface was peeled off. Example 3 is a specification in which a 2.0 m Sn film is formed on a ball having a surface hardness of HRC64, and the life is 1.5.

Elongation was 8 times, and peeling occurred on the screw shaft rolling surface. Further, Example 4 is a specification in which a Sn / 3.6 m Sn coating is formed on a ball having a surface hardness of HRC63, the life is 1.65 times longer, and peeling occurs on the screw shaft rolling surface. In addition, Example 5 is applied to a ball having a surface hardness of HRC65. 4.

The life of the Sn coating was 1.48 times longer, and the screw shaft rolling surface was peeled off.

[0056] Thus, according to the present invention, the surface hardness of the ball is made higher than the surface hardness of the rolling contact surface, and a solid lubricant film of 1 μm or more and 5 μm or less is formed on Bonore. As a result, the service life is extended. This is because even if the oil film breaks, the solid lubricant film eliminates metal contact between the balls, and the surface hardness of the ball is higher than the surface hardness of the rolling surface, thereby suppressing damage and wear of the ball. This is presumed to be due to this. In addition, since the surface hardness of the ball is higher than the surface hardness of the rolling surface, peeling occurs on the rolling surface side.

On the other hand, Comparative Example 1 is a conventional general high-load use actuator ball screw specification. In other words, the surface hardness (HRC62) is the same as the surface hardness of the rolling surface, and it is a specification that uses a ball that does not have a solid lubricating film formed on it. . In Comparative Example 2, the surface hardness of the ball is higher than the surface hardness of the screw shaft and the ball screw groove of the nut. However, since the solid lubricant film is not formed, the balls cause metal contact with each other. The surface roughness of the ball is poor and peeling occurs on the rolling surface. The force effect that should increase the surface hardness of the ball and improve the wear resistance does not appear, and the life is the same as in Comparative Example 1. Comparative Example 3 is a specification in which a solid lubricating film is formed in the configuration of Comparative Example 1, but the metal contact between the balls is eliminated, but the surface hardness of the ball is equal to the surface hardness of the rolling surface. There is little increase in the life of the ball with less improvement in wear resistance of the ball. Comparative Example 4 is a specification using a ball having a surface hardness lower than the surface hardness of the rolling contact surface and no solid lubricant film, but the balls are in metal contact with each other and the surface roughness of the ball is low. The rolling surface is lowered and the rolling surface is damaged. Further, since the surface hardness of the ball is lower than the surface hardness of the rolling surface, the ball is peeled off. for that reason, Compared with Comparative Example 1, the lifetime is considerably short.

[0058] (Second Embodiment)

FIG. 13 is a view showing a screw shaft of the ball screw and a groove cross section of the nut of this embodiment.

The cross section of the groove 111 of the screw shaft 101 is Gothic arc, i.e. the radius is the same (R)

It is a shape in which two circular arcs with different centers O and Ο are connected. Cross section of groove 121 of nut 102

11 12

Are Gothic arcs, that is, two with the same radius (R = R) but different centers O and O

2 1 21 22

These arcs are connected to each other. Further, the ratio (RZD) of the radius (R) of the cross-section arc of the grooves 111 and 121 to the diameter (D) of the ball 102 is 51.0% or more and 52.0% or less.

[0059] Then, a film made of molybdenum disulfide is formed on the surface of the ball 103 with a thickness of 0.5 μm or more and 3.0 m or less. In addition, the gap between the track formed by the grooves 111 and 121 of the screw shaft 101 and the nut 102 and the ball 103 is not less than 5 μm and not more than 70 μm. As a result, the ball screw of this embodiment has a larger load capacity and a longer life than the conventional ball screw.

In this embodiment, a solid lubricant film is formed on the ball 103. However, the groove 111 of the screw shaft 101 and the groove 121 of the nut 102 are formed without forming the solid lubricant film on the ball 103. Or may be formed in either or both of the ball 103 and the groove 111 of the screw shaft 101 and the groove 121 of the nut 102. The material of the solid lubricant film may be other than disulfurium molybdenum (for example, the one described in Patent Document 2)! /.

In this embodiment, the ball screw having a total ball structure in which the balls are in contact with each other has been described. However, the ball screw of the present invention has a holding piece 107 between the balls 103 as shown in FIG. The holding piece 107 may be arranged and held by the holding piece 107. The holding piece 107 can be obtained by molding a synthetic resin into a predetermined shape. Synthetic resins that can be used include polyamide 6, polyamide 66, polyamide 64, aromatic polyamide, etc., polyacetal resin, polyacetal resin, polybutylene terephthalate, polybutylene terephthalate elastomer, polybutylene naphthalate elastomer. The first class is mentioned. Also this These synthetic resins may be blended with glass fiber, carbon fiber, titanium fiber, strong re-wiss force, aluminum borate whisker or the like as a reinforcing material.

[0062] Examples of the shape of the holding piece include those shown in Figs. 17 and 18.

The holding piece 107 in FIG. 17 has a substantially cylindrical shape, and a concave surface 171 for receiving the ball 103 is formed on the two bottom surfaces of the column. In this holding piece 107, since the concave surface 171 has a spherical surface with a radius of curvature R larger than the radius r of the ball 103, the thickness t of the central portion with respect to the thickness L of the peripheral portion of the holding piece 107 Is getting smaller. As a result, a large number of balls 103 can be arranged in the track K, and the contact area between the balls 103 and the holding piece 107 can be reduced to reduce the sliding resistance.

[0063] The shape of the concave surface 171 of the holding piece 107 can be a Gothic arc shape in which two circular arcs are connected, or a conical shape. Alternatively, a through hole may be provided in the concave surface 171 and a lubricant may be held in the through hole to reduce the contact resistance with the ball 103. When the holding piece 107 passes through the track K and the tube 104, the outer diameter of the holding piece 10 7 can be smoothly circulated without interfering with the track K, the tube 104, and the connection portion. It is set smaller than the diameter. Specifically, the outer diameter of the holding piece 107 is preferably 0.5 to 0.9 times the diameter of the ball 103.

[0064] The holding piece 170 in FIG. 18 has a shape in which two opposite sides of the sphere are removed by a concave spherical surface 172, and the outer periphery is a convex surface. Further, the ball may be held by a member in which a plurality of holding pieces are connected by a connecting member.

Further, the ball screw of the present invention is suitable for uses such as for automobile brakes and automobile continuously variable transmissions (belt type CVT), in addition to electric injection molding machines and press machines.

[Example 6, comparative example 5]

[0065] Using a single nut tube type ball screw “: BS6316—10.5” manufactured by NIPPON SEI Co., Ltd., the radius of the arc of the gothic arc-shaped groove cross section of the screw shaft and nut (R = R = R) No bo

The life test was conducted by changing the ratio (RZD) to the 1 2 diameter (D) and the material and film thickness of the solid lubricant film as shown in Table 1 below.

For the disulfurium molybdenum coating and tin coating, use a commercially available shot-peening device, The ball was formed by adjusting the treatment time so that a film having a predetermined thickness was obtained on the ball. The thickness of these films was calculated by measuring the ball diameter before and after film formation with an electric dial gauge and dividing the difference between them by two.

[0066] The specifications of “BS6316—10.5” are as follows: Effective number of turns: 3.5 rows x 3 rows, screw shaft outer diameter: 65 mm, lead: 16 mm, ball diameter: 12.7 mm, BCD: 65 mm, single unit clearance: 20 to 30 / zm.

Each ball screw is subjected to a ball screw durability life tester manufactured by Nippon Seie Co., Ltd., test load (axial load): 300kN, stroke: 80mm, rotation speed: 500rpm, temperature: nut outer periphery temperature of 80 ° Durability life test was performed by reciprocating the ball screw under the condition of automatically supplying the lubricant “YS2 Grease” manufactured by Lube Co., Ltd. with an automatic lubricator. In this test, the distance traveled until peeling occurred in either the screw shaft, nut groove, or ball was measured as the life. Next, a relative value was calculated from the lifetime obtained for each sample, assuming that the lifetime of sample No. 10 was “1”.

These results are also shown in Table 2 below.

[0067] [Table 2]

No. R / D Solid lubricant coating life

(%) Material Thickness (m) (Relative value)

1 51.3 MoS ₂ 0.4 1.11

2 51.7 MoS ₂ 1.8 1.37

3 51.2 MoS ₂ 1.3 1.62

4 51.5 oS ₂ 2.6 1.58

5 51.5 oS ₂ 3.6 1.20

6 51. MoS ₂ 5.7 1.11

7 51.2 Sn 1.5 1.62

8 51.9 Sn 2.7 1.28

9 51.8 Sn 1.9 1.67

10 52.1 Moisture 1

11 51.6 None 0.95

12 53.2 oS ₂ 2.2 1.06

13 52.5 Sn 2.8 1.02 [0068] From this table, the ball screws No. 1 to No. 9 corresponding to Example 6 of the present invention have a longer life than No. 10 to No. 13 corresponding to Comparative Example 5. No. 1-9, the thickness of the solid lubricant film is 1. or more 2. The following is the life of No. 2-4, 7-9: 1.28 to 1.67 times that of No. 10 In contrast, the life of No. 1 with a film thickness of SO. 4 m, No. 5 with 3.6 m, and No. 6 with 5. is 1. 11 to 1.20 times. As can be seen from this result, the thickness of the solid lubricant film is preferably 0.5 / ζ πι to 3.

[0069] When the thickness of the solid lubricant film was 0.4 m, the solid lubricant film was peeled off early and the lubrication action by the solid lubricant film was lost early, so that the life improvement effect was not obtained so much. I guess that. In addition, if the thickness of the solid lubricant film exceeds 3. O / zm, the solid lubricant that has been peeled off is excessively mixed into the grease as foreign matter, so it is estimated that the service life improvement effect could not be obtained much. The

In Nos. 12 and 13, the force R / D forming the solid lubricant film with a thickness of 2.2 to 2.8 m is out of the range force of the present invention, so the life is about the same as No. 10. It was. In No. 11, the RZD was 51.6%, but the life was shorter than No. 10 because no solid lubricant film was formed.

(Third embodiment)

[0070] In the present invention, the type of the linear motion device, its specific configuration and structure are not particularly limited, and it is intended for a ball screw, a linear guide device, a linear bearing device, etc. having a holding piece. be able to.

[0071] Examples of the ball screw include the configurations shown in Figs. In the present invention, the holding piece 21 is provided with a film having lubricity on at least the surface in contact with the ball 9, preferably the entire surface, specifically, a film made of molybdenum disulfide, a soft metal, or a polymer material. Form a film. In addition, soft metal tin, gold, silver, lead, zinc, indium and their respective alloys, white metal, and the like are suitable. As the polymer material, PTGE, PTA and the like are suitable. Even if these coatings are peeled off, they are mixed with grease and develop a lubricating action. [0072] The film thickness of the coating is preferably L m to 5 m in order to ensure the effect and develop over a long period of time. A thin film of less than 1 μm may be inferior in durability, and even if a film having a thickness exceeding 5 μm is formed, the effect is saturated and uneconomical.

[0073] The method for forming a film is not limited, but the shot-peening method is suitable for forming a relatively thick film as described above while controlling the film thickness. This shot-peung method is a method in which small spheres with a particle size of several tens / zm, called a shot material, are accelerated and jetted toward the surface to be processed by the projection device, and the spheres collide with the surface to be processed at high speed. In the present invention, molybdenum disulfide, a soft metal, or a polymer material is used for the shot material and sprayed toward the holding piece 21 mm. In general, the shot peening method tends to make the surface of the coating rough, and therefore the coating surface may be smoothed as necessary.

[0074] The holding piece 21 can be made of a synthetic resin, such as polyamide 6, polyamide 66, polyamide 46, polyamide polyamide such as aromatic polyamide, polyacetal resin, polybutylene terephthalate, polybutylene terephthalate. It is obtained by molding an elastomer, polybutylene naphthalate-based elastomer or the like into a predetermined shape. These synthetic resins are also used for reinforcement.

Glass fiber, carbon fiber, titanium fiber, potassium whisker, aluminum borate whisker, etc. may be blended.

[0075] The shape of the holding piece 21 is not particularly limited. However, as shown in the sectional view of Fig. 4, the concave spherical surface 23 having a radius of curvature R larger than the radius r of the ball 9 on both sides 23 It can be in the shape of a disk formed with. By adopting such a shape, the thickness t of the central portion becomes smaller than the total thickness L, and more balls 9 can be disposed, and the contact area between the balls 9 and the holding piece 21 Can be reduced to minimize sliding resistance.

In addition, the shape of the concave spherical surface 23 may be a Gothic arch-shaped concave surface formed by intersecting two arcs at an intermediate portion, or a conical concave surface. Also, provide a through hole in the concave surface or hold a lubricant in the through hole to reduce the contact resistance with the ball 9.

[0077] In addition to the above, the holding piece 21 may have a cross-sectional shape as shown in FIG. 5, or a plurality of holding pieces 21 connected by connecting members 22 as shown in FIG. It is. Similarly, any of the holding pieces 21 is formed with the above film. As described above, the ball screw has been exemplified and described with respect to the embodiment of the present invention. However, for a linear guide or the like which is another linear motion device, the operability is improved by inserting a similar holding piece. Can be planned.

For example, the force shown in FIG. 7 is an example of a linear guide. This linear guide includes a guide rail 31 having a rolling groove 32 on its outer surface, and a slider 35 assembled across the guide rail 31. . A ball circulation path is formed inside the slider 35 with the rolling groove 32 of the guide rail 31, and the ball and the coating film are formed inside the ball circulation path as described above. The pieces are housed so that they can roll!

[0080] [Examples 7 to 9, Comparative Examples 6 to 7]

As shown in Table 3, a holding piece with different specifications was incorporated into a ball screw manufactured by Nippon Seige Co., Ltd. (specifications are as follows), and torque measurements were performed to evaluate operability. The holding piece is made of greaves, and a commercially available shot peening machine is used as the shot material. In Example 7, disulfurized molybdenum fine particles having an average particle diameter of 1 μm, and in Example 8, the average particle diameter of 2.5 μm. A film was formed using m fine tin particles, and in Example 9, PTFE fine particles having an average particle diameter of 3 m. In Comparative Example 6, the total ball specification does not include a holding piece, and in Comparative Example 7, the film is not formed and the holding piece is used as it is.

• NIPPON SEI Co., Ltd. Ball Screw BS3610—2.5 (No .: 36 10 300—7)

'Shaft diameter: 36mm

• Lead: 10mm

• BCD: 37mm

'Bonore diameter: 6. 35mm

• Effective number of turns: 2.5 turns X I row

'Torque measurement speed: lOrpm

• Stroke: 100mm

• Test load: 8800N axial load is applied to the double nut panel.

[0081] The force operability shown in Fig. 8 to Fig. 12 is measured based on the fluctuation range of the torque. The operability is bad! From "X" → "△" → "○" → "◎" It was evaluated in four stages. The results are shown in Table 3. [0082] [Table 3]

Note) Operability evaluation: Poor operability “X” → “△” → “◯” → “◎” Good operability

[0083] As shown in Table 3, the operability was the worst in Comparative Example 6 without the holding piece interposed. Even in the specification with the holding piece inserted, in Comparative Example 7, no film is formed!

On the other hand, according to the present invention, in each of the examples in which the holding piece on which a coating film having a sulfur disulfide molybdenum, tin, or PTFE force is formed is interposed, the operability is greatly improved.

[0084] (Fourth embodiment)

FIG. 19 is a cross-sectional view of the main part showing the peripheral portion of the end of the tube.

As shown in FIGS. 1, 2, and 19, the ball screw 1 includes a screw shaft 3 having a helical screw groove 3a on the outer peripheral surface and a helical screw groove 5a facing the screw groove 3a of the screw shaft 3. A nut 7 provided on the inner peripheral surface, and a plurality of balls 9 movably loaded in a spiral ball rolling path 77 formed by both screw grooves 3a and 5a. Then, when the nut 7 and the screw shaft 3 are rotated relative to each other by being screwed onto the screw shaft 3 via the ball 9, the screw shaft 3 and the nut 5 are axially moved via the rolling of the ball 9. It is designed to move relative. The cross-sectional shape of the thread grooves 3a, 5a may be an arc shape or a gothic arc shape! /.

[0085] A part of the outer peripheral surface of the nut 7 is cut out to form a flat surface portion 13. A tube 15 that forms an endless ball circulation path by communicating the starting point and the end point of the ball rolling path 77 is fixed to the flat portion 13 by a tube presser 17. When the ball 9 moves in the ball rolling path 77 and turns around the screw shaft 3 a plurality of times and reaches the end point of the ball rolling path 77, the ball 9 is scooped up from one end of the tube 15 and moved to the tube 15 Through the inside, the other end force of the tube 15 is also returned to the starting point of the ball rolling path 77. In this way, the ball 9 rolling in the ball rolling path 77 is circulated indefinitely by the tube 15. Therefore, the screw shaft 3 and the nut 7 can continuously move relative to each other.

[0086] The tube 15 corresponds to a ball return path which is a constituent of the present invention. Further, the material of the tube 15 is not particularly limited, but a resin is preferably a resin. The ball return path may be manufactured by Xia-Ji, or may be formed by molding if the material is grease, or by pressing if the material is metal.

The inner surface of the tube 15 is covered with a solid lubricating film (not shown) consisting of at least one of molybdenum disulfide and an organic molybdenum compound. This solid lubricating coating may be further coated on the groove surfaces of both screw grooves 3a and 5a. Since it has such a solid lubricating film, the ball screw 1 is used under conditions where a high load is applied and a moment load is applied, and the ball 9 is rubbed against the inner surface of the tube 15 with an excessive force. Even if this occurs, the inner surface of the tube 15 is less likely to be damaged, such as abrasion or peeling. Therefore, poor circulation of ball 9 is unlikely to occur!

[0087] In addition, since the inner surface force of the tube 15 is less likely to generate wear powder or peeling powder, the thread grooves 3a, 5a and the ball 9 are not easily peeled off due to the entanglement of foreign matter. Therefore, the ball screw 1 has a long life. Even if the solid lubricant film is peeled off by rubbing the balls 9, the release powder of the solid lubricant film diffuses into the grease and acts as a solid lubricant, so that the lubricating action of the grease is improved.

[0088] Such a ball screw 1 can be suitably used in a mold clamping mechanism of a mold clamping apparatus incorporated in an electric injection molding machine or a press machine. That is, it is suitable as a ball screw in a mold clamping mechanism that performs mold clamping of the mold clamping device by driving the ball screw with an electric motor. However, the use of the ball screw of the present invention is not limited to the above. Specific examples of the organomolybdenum compound include molybdenum dialkyldithiodicarbamate molybdenum and molybdenum dialkyldithiodiphosphate. However, the solid lubricant film may be composed of soft metal, polymer material, metal oxide, metal nitride, metal carbide, clay mineral, lead zirconate titanate (PZT), and solid lubricant.

[0089] Specific examples of the soft metal include gold, silver, lead, zinc, tin, and indium. Specific examples of the polymer material include polytetrafluoroethylene (PTFE) and perfluoroalkoxy fluorine resin (PTA). Furthermore, as a specific example of the metal oxide, Examples thereof include SiO 2, Al 2 O 3, MgO, TiO 2 and ZnO. Specific examples of metal nitride include Si

2 2 3 2 3

N, ZrN, CrN, TiAIN are examples. Specific examples of metal carbides include SiC, TiC,

Four

WC is given. Specific examples of clay minerals include bentonite, smectite, and mica. Specific examples of solid lubricants include graphite, BN, and WS.

2

[0090] The method for forming the solid lubricant film is not particularly limited, but a method in which fine particles of disulfurium-molybdenum or organic molybdenum-molybdenum compound collide with the surface to be treated is preferable. For such treatment, a method of spraying fine particles together with a gas, such as a shot peening method or a sandblast method, or a centrifugal projection method can be used.

In the ball rolling path 7, grease (not shown) for lubricating the groove surfaces of both screw grooves 3a and 5a and the surface of the ball 9 is disposed. The type of grease is not particularly limited, but examples include greases using mineral oil, ester-based synthetic oil, ether-based synthetic oil, hydrocarbon-based synthetic oil, or the like as a base oil. The grease may contain additives such as a thio-based extreme pressure agent, a sulfur-phosphorus-based extreme pressure agent, and an organometallic compound-based extreme pressure agent containing io, phosphorus and zinc.

[0091] Plastic dust seals 19 may be disposed at both ends of the nut 7. This prevents foreign matter from entering the nut 7 from the outside.

Further, as shown in FIG. 2, a holding piece 21 for preventing contact between the balls 9 may be interposed between the adjacent balls 9. Then, since the competition between the balls 9 is eliminated, the movement of the balls 9 is performed more smoothly. Therefore, the circulation performance of the ball 9 and the feeding accuracy of the ball screw 1 are excellent, and the generation of noise and vibration is further suppressed. The material of the holding piece 21 is not particularly limited. For example, a polyamide having a lubricating action on its own is a fluorine resin, or polyethylene impregnated with a lubricating oil.

[0092] [Examples 10 to 13, Comparative Examples 8 to 9]

Hereinafter, the present invention will be described with reference to more specific examples. The ball screw BS6316—10.5 (Nominal: 63 X 16 X 300—Ct7) manufactured by NIPPON SEI CO., LTD. Having the same configuration as the ball screw 1 described above, A durability test was conducted.

The specifications of this ball screw are as follows. • Screw shaft diameter: 63mm

• Li ~~ do: 16mm

'Bonore diameter: 12.7mm

• Number of circuits: 3.5 卷 X 3 rows

'Axial load: 300kN

'Crushing moment load: 4.2 kN-m

'Holding piece: Yes

The ball screws of Examples 10 to 13 and Comparative Examples 8 and 9 subjected to the durability test differed in the tube material and the type of solid lubricant film (see Table 4). The ball screw was lubricated by automatically supplying YS2 grease from Lube Co., Ltd. with an automatic lubricator.

[0093] [Table 4]

*) Metal stamping products

Next, the ball screw durability test will be described. The ball screw is mounted on a ball screw endurance tester manufactured by Nippon Seige Co., Ltd. and rotated to rotate the screw shaft thread groove, nut thread groove or ball, or ball circulation failure. The distance traveled until the ball screw malfunctions due to was taken as the life of the ball screw. Table 4 shows the test results. The life values in Table 4 are relative values when the life of the ball screw of Comparative Example 1, which is a general ball screw, is 1.

[0095] As can be seen from Table 4, the ball screws of Examples 10 to 13 had a longer life than the ball screws of Comparative Examples 8 and 9 in which the inner surface of the tube was not coated with a solid lubricant film. The ball screws of Examples 10, 12, and 13 were peeled off in the thread groove of the screw shaft, and the ball screw of Example 11 As for the screw screw, peeling occurred in the thread groove of the nut.

Further, in the ball screw of Comparative Example 8, the inner surface of the tube was worn, resulting in malfunction of the ball screw due to poor circulation of the ball. Further, in the ball screw of Comparative Example 9, the inner surface of the tube was peeled off, resulting in malfunction of the ball screw due to poor circulation of the ball.

In the examples, the RZD ratio is not set to different values for the male screw groove and female screw groove. Because of this curved surface, the contact stress approximated to the male thread groove is RZD54%. (This difference varies depending on the ball diameter, etc.) Thus, there is no problem even if the RZD of the female thread groove is larger than that of the male thread groove.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

This application consists of a Japanese application filed on March 25, 2005 (Japanese Patent Application 2005-88323), a Japanese application filed on March 25, 2005 (Japanese Patent Application 2005-88324), and a Japanese application filed on March 28, 2005. This is based on the application (Japanese Patent Application 2005-923 75) and the Japanese application filed on January 19, 2006 (Japanese Patent Application 2006-11765), the contents of which are incorporated herein by reference.

Industrial applicability

The ball screw of the present invention is suitable for an actuator, for example, and is particularly suitable for applications that are relatively large and subject to a high load such as an actuator such as an electric injection molding machine or a press machine.

In conventional ball screws, the lower limit of the groove R ratio was about 52% from the viewpoint of adverse effects of slipping, but by applying MoS coating to the ball, the tangential force can be suppressed, and 51.5%

2

Even the degree of groove R can prevent early damage due to the adverse effects of slipping. By reducing the groove R, the surface pressure can be reduced, the load capacity can be increased, and the life of the high-load ball screw can be extended.

Claims

The scope of the claims

[1] A screw shaft having a spiral groove formed on the outer peripheral surface, a nut having a spiral groove formed on the inner peripheral surface, and a screw shaft groove and a nut groove are formed to face each other. In a ball screw comprising a track, a return path connecting the end point and the start point of the track, and a plurality of balls arranged in the return path and in the track,

At least one of the screw shaft and nut

[2] The surface hardness of the ball is higher than the surface hardness of the ball screw groove of the screw shaft and the ball screw groove of the nut, and a film of 1 μm or more and 5 μm or less on the surface of the ball 2. The ball screw according to claim 1, wherein a solid lubricant film is formed with a thickness.

[3] The ball screw according to claim 2, wherein the solid lubricant film is made of molybdenum disulfide or a soft metal force.

4. The ball screw according to claim 3, wherein the soft metal is selected from tin, gold, silver, zinc, indium and alloys thereof.

5. The ball screw according to any one of claims 1 to 4, wherein the surface hardness of the ball is HRC63 or more.

[6] At least! / ヽ deviation of the screw shaft and the nut is:

The groove has a Gothic arc cross section (a shape in which two arcs having the same radius and different centers are connected), and the arc forming the Gothic arc of the groove cross section with respect to the ball diameter (D). The ratio of radius (R) (RZD) is 51.0% or more and less than 52.0%,

2. The ball screw according to claim 1, wherein a solid lubricant film is formed on a surface of at least one of the groove of the screw shaft, the groove of the nut, and the ball.

7. The ball screw according to claim 6, wherein a gap between the ball and the track is not less than 5 μm and not more than 70 μm, and a thickness of the solid lubricant film is not less than 0.5 m and not more than 3.0 m.

8. The solid lubricant film according to claim 6 or 7, wherein the solid lubricant film is made of molybdenum disulfide or tin. Bonore screw.

[9] The Bonore screw according to any one of claims 6 to 8, wherein a holding piece is disposed between the balls.

[10] The holding piece interposed between the balls, and one end side force of the ball groove and a circulation path for circulating the ball to the other end side of the ball groove, 2. The linear motion device according to claim 1, wherein a film made of molybdenum disulfide, soft metal, or polymer material is formed on at least a surface of the piece that contacts the ball.

11. The ball screw according to claim 1, wherein the inner surface of the ball return path is coated with a solid lubricating film consisting of at least one of disulfurium molybdenum and organic molybdenum compound. .

[12] The ball screw according to [11], wherein the ball return path is made of grease.

13. The ball screw according to claim 11, wherein the ball return path is constituted by a resin member manufactured by injection molding.

14. The ball screw according to claim 11, wherein the ball return path is made of metal.

15. The ball screw according to claim 11, wherein the ball return path is made of a metal member manufactured by metal pressing.